Drill bit

ABSTRACT

An improved drill bit tooth having a leading tooth face, i.e., the face first contacting the formation being cut, substantially parallel with the axis of rotation of the drill bit cone. The trailing face of the tooth is convexly shaped to act as a fulcrum. This tooth configuration allows the tooth to get under and lift a chip from the formation being cut, rather than sliding it to the side.

United States Patent 1191 [11] 3,743,038 Bennett July 3, 1973 [54] DRILL BIT 1,388,456 8/1921 Fletcher 175/353 1.412.003 4/1922 Hughes 175/331 [751 mm Demo"! 2.058.750 10/1936 Williams et al. 175/376 x [731 Assignee= 'P (Delaware), FOREIGN PATENTS OR APPLlCATlONS a 563.402 2 1944 Great Britain l75/378 [22] Filed: Nov. 23, 1971 Primary Examiner-David H. Brown PP'- 2013516 -G o ge L, Church, James D. Olsen ct al- [52] US. Cl 175/341, 175/353, 175/374 7 BST [51] Int. Cl. E2lb 9/10, E21c 13/02 [5 A 58 Field of Search 175/327, 331, 332. havmg a leadmg facet 75/336 341, 344, 353 354, 374473 i.e., the face first contacting the formation being cut. substantially parallel with the axis of rotation of the 56] References Cited drill bit cone. The trailing face of the tooth is convexly shaped to act as a fulcrum. This tooth configuration al- UNITED STATES PATENTS lows the tooth to get under and lift a chip from the for- 1 3:31 a] 1.75/34 mation being cut, rather than sliding it to the side. e 1,694,679 12/1928 Black..... I 1 Claim, 3 Drawing Figures PATENIED JUL3 I973 v INVENTOR JOHN D. BENNETT DRILL BIT BACKGROUND OF THE INVENTION This invention relates to a rotary earth boring drill bits and especially relates to a novel drill bit tooth.

At the present time, most drill bits are remarkably similar, having a bit body having a hollow interior and three shank like protrusions on the lower end of the bit body. Cones are rotatably attached to each shank. Each cone is ringed with teeth and the cones are positioned with respect to each other so that the teeth of adjacent cones partially intermesh with each other. Located between the shanks are nozzles through which the drilling fluid passes for removal of cuttings separated by the drill bit teeth. These nozzles are housed in nozzle bosses which cause a bulge of the housing between the shanks of the drill bit. Drilling fluids pass through the interior of the drill pipe and into the drill bit, whereupon drilling fluids exit the drill bit by way of the nozzles and travels downwardly into contact with the formation being drilled. The distance between the nozzles and the formation is a matter of several inches. As portions of the formation are separated from the formation matrix by the bit teeth, the drilling fluid sweeps the cuttings from the bottom of the wellbore and returns them to the surface by way of the annular space between the drill pipe and the wellbore.

Laboratory tests have shown that the drilling fluid exerts a strong hold-down force on the cuttings, thereby aggravating the work require by the drill bit. The drilling fluid penetrates crevices in the formation through which the cut is being made which serves to hold the formation pressure in check thereby preventing inflow of gas or oil. Normally, the weight of the drilling fluid is maintained at a level such that the hydrostatic head of the drilling fluid column in the wellbore is sufficient to maintain a positive differential back pressure on the formation in excess of the expected formation pressure. Use of the drilling fluid therefore maintains the well in a dead condition throughout the drilling operation with the circulating pressure of the drilling fluid preventing the inflow of formation fluids. The drilling fluids not only forms a cake about the borehole wall, but also forms a cake at the bottom of the borehole being drilled by the drill bit. As the bit grinds into the earth formation, the mud is being continuously applied to the bottom of the hole so that a positive back pressure is maintained against the formation being drilled. Such a positive pressure on the formation is a direct deterrent to the removal and lifting of cuttings from the borehole, with the pressure tending to hold the cuttings down rather than permitting their removal to the surface with the circulating drilling fluid.

As drill bit teeth are presently designed, the action of the tooth causes a small portion of the formation to be pushed to the side and thereby become separated from the remainder of the formation matrix. It is apparent that the sideward movement of the portion of the formation being cut is resisted by the formation matrix as the formation portion is compacted against it. The pressure of the drilling fluid also acts to aggravate the work required to remove the formation portion. Since present drill bit teeth are symetrically shaped, and are generally either round or wedge shaped, there are basically horizontal forces being applied against the formation. The weight on the drill bit supplied-by drill collars or drill pipe usually results in some penetration of the formation at the bottom of the wellbore, therefore, the main force necessary to sever formation portions from the formation matrix must come from rotation of the drill string. Such rotation results in the drill bit teeth serially contacting the formation, so that each tooth pushes formation portions sideways and severs them from the formation matrix. It would be advantageous to design a drill bit tooth such that the tooth would get under the formation portion and lift it from the formation matrix. The advantage would be two fold in that the drilling fluid could get between the formation matrix and the formation portion thereby neutralizing th'e hold-down force and additionally the formation matrix would not resist removal of formation portions since it no longer would be directly in the removal path followed by formation portions.

It is therefore an object of the present invention to provide a drill bit with a new and improved drill bit tooth.

SUMMARY OF THE INVENTION With this and other objects in view, the present invention contemplates the drill bit tooth having a leading edge substantially parallel to the diameter of the cone to which the tooth is attached. The trailing edge of the drill bit tooth may be of a convex shape so that it operates as a fulcrum to provide mechanical advantage.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view of a drill bit;

FIG. 1A is an elevational view of a portion of the drill bit shown in FIG. 1, which illustrates in greater detail the action of the drill bit tooth on the formation;

FIG. 2 is a view of the bottom of a drill bit which illustrates one cone of the drill bit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1 of the drawings, the drill bit 10 is depicted having a housing 28 having a hollow interior and including a plurality of shanks 14 formed thereon and extending below the main housing 28. R0- tatably attached to the shanks 14 are cones 18 having teeth 16 formed thereon. The cones 18 are attached to journals formed on the shanks 14. The drill bit housing 28 has an upper end 12 which is threaded so that it can be attached to drill pipe. The drill bit 10 is shown engaging formation 20 which is shown having formation portions 21 being acted on by the drill bit teeth 16. The direction of rotation of the drill bit has been indicated by arrow 32 and has been depicted to be in a clockwise direction. If the teeth 16 formed on cones 18 are engag ing formation 20, the teeth 16 will serially engage the formation 20 because the cones are free to rotate on the journals of the shanks 14. Thus, the cones with attached teeth, rotate in a counterclockwise direction. The direction of rotation of the drill bit cone 18 with attached teeth 16 has been indicated by arrow 34. The shape of the drill bit teeth 16 is most easily seen by reference to FIG. 2, however, for present purposes they are shown as presenting a tooth face parallel to the axis of rotation of the cones 18.

In the operation of the drill bit 10, as the drill pipe is rotated in thedirection indicated by arrow 32 the bit is also rotated since it is attached to the drill pipe at threaded connection 12. Since the cones 18 are free to rotate the drag on the teeth 16 will cause rotation of the cones with attached teeth in a counterclockwise direction as indicated by arrow 34. Because of weight on the bit usually supplied by drill collars, the drill bit teeth will tend to penetrate the formation 20. As the cones 18 with attached teeth 16 rotates, the formation portions 21 are removed from the formation matrix 20 by the upward action of the teeth 16.

The shape of the drill bit teeth 16 facilitates more efficient dislodgement of formation portions 21 from the matrix 20, as can be better illustrated by referring to FIG. 1A. FIG. 1A depicts only the portion of the drill bit in the vicinity of the formation being cut. Teeth 16 are shown having leading edges 24 which lie in planes parallel to the axis of rotation of the cone 18. The trailing edges 26 of the teeth 16 are convexly shaped to provide support for the leading edges 24. Additionally the convex shape allows the trailing side of the teeth to act as a fulcrum in wedging formation portions 21 from the formation matrix 20. A vertical section of each tooth 16 taken at right angles to the cone axis generally describe quarter circles. Horizontal sections of each tooth describe rectangles'which decrease in area towards the portion of the tooth 16 furtherest from the axis of the roller cutter. The entire tooth design can best be seen by referring to FIG. 2. Referring back to FIG. 1, the direction of rotation of the shank 14 is illustrated by arrows 32 and the resulting direction of rotation of the cone with attached teeth 16 is in direction shown by arrow 34.

As the drill pipe is rotated, which for illustrative purposes is shown to be in a clockwise direction as indicated by arrow 32, the cone 18 with attached teeth 16 will rotate in a counterclockwise direction indicated by arrow 34 because of the drag of the engagement of the teeth 16 with formation 20. As the teeth 16 serially engage the formation 20, the formation portions 21 are dislodged from the formation matrix. Because of the angle at which the teeth 16 contact the formation 20 a more efficient removal of formation portions 21 is effected. The novel design of the drill bit tooth 16 results in the tooth tending to lift the formation portion 21 from the matrix rather than force segments to the side as in the case with conventional drill bit teeth. The tooth as shown in FIG. 1A will tend to get beneath the formation portion 21 and lift it from the formation matrix 20. The trailing edges 26 of the teeth 16 have been shown as having a convex configuration which serves the dual purpose of providing mass for a stronger tooth as well as to serve as a fulcrum to aid in the dislodgement of the formation portion 21. It is of course contemplated that the trailing edge of the tooth 16 may also lie in a flat plane in lieu of its being convexly shaped. The angle at which the trailing edge lies relative to the axis of rotation of the cone 18, should be fairly large so that the teeth 16 will have sufficient mass to withstand high drill weights and extremely hard formations. additionally, the trailing edges 26 can be made of a material softer than the leading edges 24 such that the teeth 16 are self sharpening. Although the: leading edges 24 of teeth 16 are shown to be lying in planes parallel to the axis of rotation of the cone 18, it is contemplated that the leading edge of the teeth could be designed so that it contacts the formation 20 at an angle greater than degrees. In such a configuration the greater the angle that the tooth strikes the formation results in more effective lifting of the formation portions 21 from the matrix 20. Of course, the required strength of the teeth 16 would limit the severity of the angles used.

Referring next to FIG. 2, there is depicted the bottom view of a conventional drill bit utilizing the improved drill bit teeth. Only one cone 18 has been shown in detail with only the outline of the other cones being shown. This bit is a conventional jet bit which is almost universally used in present oil well drilling. The mud jet 30 can be seen between two adjacent cones 18. This jet nozzle is located adjacent the upper side of the cone. The-re are a series of three rows of teeth which are formed in the manner described previously in FIGS. 1 and 1A. As configured, the cone is meant to rotate in the direction shown by the arrow 34. In the operation of this type of drill bit, the bit is rotated on the formation at the bottom of the wellbore causing serial engagement of the teeth 16 with the formation 20. The rotating teeth dislodge portions of the formation matrix. As these formation portions are dislodged the mud exiting jet nozzles 30 sweeps the cuttings from the bottom of the borehole to the surface by way of the annular space between the drill pipe and the borehole. As can be readily seen by FIG. 2, the leading edges of the teeth 16 lie in planes parallel to the axis of rotation of the cone 18. As illustrated by FIG. 1, the angle of the leading edge of the teeth 16 allows the tooth to get under the formation portion 21 so that the drilling fluid can get beneath the formation portion and thereby neutralize the drilling fluid hold-down force. Such neutraliztion of the hold-down force greatly reduces the horsepower requirements needed to rotate the drill bit 10, thereby resulting in substantial savings.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects, and therefore the aim in the appended claims is to cover all such changes and modifications that fall within the true spirit and scope of this invention.

What is claimed is:

l. A drill bit comprising: a bit body, a plurality of cone shaped roller cutters rotatably attached to the bit body; and a plurality of teeth formed on each cone shaped roller cutter, wherein each tooth has a front tooth face lying in a plane substantially parallel to the axis of rotation of the roller cutter on which the tooth is formed and wherein each tooth has a rear tooth face which is convexly shaped so that a vertical section of each tooth taken at right angles to the cone axis generally describes a quarter circle, and horizontal sections of each tooth describe rectangles which decrease in area towards the portion of the tooth furtherest from the axis of the roller cutter. 

1. A drill bit comprising: a bit body, a plurality of cone shaped roller cutters rotatably attached to the bit body; and a plurality of teeth formed on each cone shaped roller cutter, wherein each tooth has a front tooth face lying in a plane substantially parallel to the axis of rotation of the roller cutter on which the tooth is formed and wherein each tooth has a rear tooth face which is convexly shaped so that a vertical section of each tooth taken at right angles to the cone axis generally describes a quarter circle, and horizontal sections of each tooth describe rectangles which decrease in area towards the portion of the tooth furtherest from the axis of the roller cutter. 